This sounds like a new warning from clang that the JUCE code is not yet disabling when including the AAX headers. Could you copy-paste the output of compiling include_juce_audio_plugin_client_AAX.mm?
its not Juce yet its just compiling the AAX DEV sdk libs that avid provides for aax development on a mac. I compiled them on windows using visual studio 2017 and it worked.
I will post the entire error message later when I get back to my mac.